In the fields of the electronic and electrical industry and the automobile, aircraft and space industries, there is a strong demand in recent years for crystalline, thermoplastic resins having high heat resistance of about 300.degree. C. or higher in terms of melting point and moreover easy melt processability.
Recently, poly(arylene thioetherketoneketones) (hereinafter abbreviated as "PTKKs") have drawn attention for their high melting points. Various studies are now under way thereon.
There are some disclosure on PTKKs, for example, in U.S. Pat. No. 3,442,857, German Offenlegungsschrift 3405523 A1, Japanese Patent Laid-Open No. 27434/1987, U.S. Pat. No. 4,795,799, Japanese Patent Laid-Open No. 120720/1985, etc.
Regarding the PTKKs described in the above publications, neither molding nor forming has however succeeded to date in accordance with conventional melt processing techniques. Incidentally, the term "conventional melt processing techniques" as used herein means usual melt processing techniques for thermoplastic resins, such as extrusion, injection molding and melt spinning.
The unsuccessful molding or forming of PTKKs by conventional melt processing techniques is believed to be attributed to the extremely high melting points of the conventional PTKKs, which was about 410.degree. C., so that a high melt processing temperature was needed. They therefore tended to lose crystallinity or to undergo crosslinking and/or carbonization, resulting in a rapid increase in melt viscosity, upon their melt processing.
PTKKs contain two ketone groups in each recurring unit and are hence inferior in solvent resistance and moisture absorption resistance. A limitation is therefore unavoidably posed on their application fields as heat-resistant resins. Moreover, these PTKKs are generally obtained as fine powders. This has led to an additional problem upon their production such that they show poor handling properties in their collection step after polymerization, especially in filtration, washing, drying and transportation. Still further problems have also arisen such as poor metering property upon melt processing and occurrence of blocking in hoppers or the like.
On the other hand, as poly(arylene thioethers) (hereinafter abbreviated as "PATEs"), for example, poly(p-phenylene thioether) has found utility as a high-performance engineering plastic having heat resistance and solvent resistance. It can be obtained by reacting dichlorobenzene and sodium sulfide, which are both very inexpensive monomers readily available on an industrial scale (Japanese Patent Publication No. 12240/1977). However, the melting point of its crystals is below 300.degree. C. and its glass transition temperature (Tg) is as low as about 90.degree.. There is hence an outstanding desire for the development of polymers having high melting point and high Tg.